Variable resistor

ABSTRACT

A variable resistor comprising a resistor element, a slide contact member in sliding engagement with said resistor element, and switch means actuated by said slide contact member. The switching means connects one end of the resistor element to ground or to an open circuit terminal when slide contact engages the other end of the resistor element.

United States Patent [191 Oct. 29, 1974 Ashiya et a1.

VARIABLE RESISTOR Q Inventors: Takechika Ashiya, Kawasaki; MasaruNagami, Yokohama; Yoshimi Watanabe, Tokyo, all of Japan Assignee: SonyCorporation, Tokyo, Japan Filed: Oct. 19, 1973 Appl. No.: 408,105

Foreign Application Priority Data Oct. 24, 1972 Japan 47-122924 US. Cl338/200, 307/156, 323/80, 330/30, 33'8/128, 338/172, 338/202 Int. Cl1101c 9/08 Field of Search 338/200, 201, 198, 191,338/185,178,128,129,131,179, 92, 95, 120, 127, 162, 172, 173, 174, 190,202; 323/63, 80, 94; 307/98, 156, 42, 43; 333/6; 317/99; 330/185, 191,144, 147, 30, 69, 74,

[56] References Cited UNITED STATES PATENTS 1,931,799 10/1933 Hunter323/80 X 2,783,397 2/1957 Lauson 338/128 2,942,221 6/1960 Di Girolamo,338/200 3,047,825 7/1962 Biltz 338/172 3,375,446 3/1968 Guyton 338/198 X3,587,027 6/1971 Gerwitz 338/198 X 3,629,775 12/1971 Kindred 338/1283,633,146 1/1972 Sasaki et a1 338/200 X.

Primary Examiner-Bruce A. Reynolds Attorney, Agent, or Firm-Hill, Gross,Simpson, Van Santen, Steadman, Chiara & Simpson [57] ABSTRACT A variableresistor comprising a resistor element, a slide contact member insliding engagement with said resistor element, and switch means actuatedby said slide contact member. The switching means connects one end ofthe resistor element to ground or to an open circuit terminal when slidecontact engages the other end of the resistor element.

7 Claims, 12 Drawing Figures VARIABLE RESISTOR BACKGROUND OF THEINVENTION 1. Field of the Invention The present invention relatesgenerally to a variable resistor, and more particularly to a variableresistor with a slide contact member engageable with a resistor elementwhich receives two different signals applied to opposite ends of theresistor element so as to derive from the slide contact member either ofthe two different signals or alternatively a mixture of the two signals.

2. Description of the Prior Art FIG. 1 shows a mixing circuit in which aconventional variable resistor 1 is employed. The variable resistor 1consists of a resistor element In and a slide contact member 6. Contactpoints 11 and 1.2 are provided at opposite ends of the resistor elementla and a microphone amplifier 2 is connected to contact 11 and anequalizer amplifier 3 (which will be hereinafter referred as to an Eamplifier) is connected to contact 12. The amplifiers may be suppliedwith audio signals, respectively. Thus, signals from a microphone orother device are applied to the amplifiers 2 and 3 for amplification,delivery to an output terminal 4 through slide contact member 6, as aselected single signal or a mixed signal.

As the slide contact member 6 moves on the resistor element la, theoutput signal is adjusted. When the slide contact member 6 movestocontact point 11, the signal from the microphone amplifier 2 isdelivered directly unattenuated to the output terminal 4 without passingthrough the resistor element 1a. When slide contact 6 engages contactpoint 12, the signal from E0 amplifier 3 is passed unattenuated tooutput terminal 4. When slide contact 6 is at an intermediate point ebetween contact points 11 and 12, a mixture of the two input signals issupplied to output terminal 4.

In prior art devices according to FIG. 1, there is a defeet in that ifthe resistance value of the resistor element la is not selected largeenough as compared with the output impedances of the microphoneamplifier 2 or the EQ amplifier 3, separation of the two signals fed tothe contact points '11 and 12 cannot be satisfactorily achieved even ifthe slide contact member 6 engages the contact points 11 and 12.

Further, when the slide contact member 6 is positioned at intermediateor mid-point c, it is necessary that the resistance value of theresistor element la be small as compared with the input impedance of adevice which may be connected to the output terminal 4 so as to avoidthe attenuation waveguide the output signal; otherwise, the separationcharacteristics between the two signals, when the slide contact member 6is positioned at the contact point 11 or 12, will be deteriorated.

SUMMARY OF THE INVENTION An object of this invention is to provide animproved variable resistor with a switching means.

Another object of this invention is to provide an improved variableresistor which comprises a resistor element, a slide contact meansmovable on the resistor element, and a switch means which is controlledby movement of the slide contact means relative to the resistor elementsso as to ground or open circuit, one end of the resistor element whenthe slide contact means reaches the other end of the resistor element,whereby the signal separation characteristic between two applied signalsis improved.

A further object of this invention is to provide a variable resistor foruse as a mixing circuit which mixes two different signals.

A yet further object of this invention is to provide a variable resistorfor use as a mixing circuit which mixes a two-channel signal with asignal from a microphone.

The other objects, features and advantages of this invention will becomeapparent from the following description taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a circuit diagram showing amixing circuit using prior art variable resistor;

FIG. 2 is a side plan view showing an embodiment of the variableresistor according to this invention;

FIGS. 3A, 3B and 3C are respectively plan views of parts used in thevariable resistor depicted in FIG. 2;

FIG. 4 is a circuit diagram showing an example of a mixing circuit inwhich the variable resistor of this invention is used;

FIG. 5 is a circuit diagram showing a two-channel stereophonicreproducing apparatus in which the variable resistor of this inventionis used;

FIG. 6 is a circuit diagram showing another example of a mixing circuitin which the variable resistor of this invention is employed;

FIG. 7 is a perspective view showing another example of the variableresistor according to this invention; and

FIGS. 8A, 8B and 8C are respectively schematic diagrams for explainingthe variable resistor shown in FIG.

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of this inventionis shown in FIGS. 2-l2 in which the same reference numerals used in FIG.1 designate similar elements.

The variable resistor I of this invention consists of the resistorelement la and a slide contact member 6 engageable with the resistorelement la as in the case of FIG. 1. In this invention, when the slidecontact member 6 approaches or contacts the contact point 11 of theresistor element 1a, its other contact point 12 will be opened orgrounded by a switching means, and when the slide contact member 6approaches or contacts the other contact point 12 of the resistorelement la, the other contact point 11 will be opened or grounded by aswitching means.

In FIGS. 2, 3A, 3B and 3C, reference numeral 7 indicates a rotary shaftmade of insulating material which has attached thereto at its one end aknob 7a and is rotatably supported by disc-like substrates 8, 9 and 10.The resistor element la is ring-shaped with a gap and is coaxiallymounted on the substrate 8. The contact points 11 and 12 are provided atthe opposite ends of the resistor element la and are in electricalcontact therewith. The output terminals of the microphone amplifier 2and EQ amplifier 3 are connected to the contact points 11 and 12,respectively. The conductive slide member 6 has one end fixed to therotary shaft 7 and its other end is in slide contact with resistorelement la. Member 6 also engages the contact points 11 and 12 at itsend travel to produce a composite signal from the outputs of themicrophone and EQ amplifiers 2 and 3 or alternatively their signalsseparately if the position of the slide contact member 6 engages contactpoints 11 and 12. A flexible lead can be connected between contactmember 6 and output terminal 4.

A connecting member is made of conductive material and is similar to theresistor body la in shape being ring-shaped with a gap. Member 15 ismounted on the disc-shaped substrate 9 coaxially with the rotary shaft7. A contact point 17 is electrically connected to one end of theconnecting member 15. A contact point 18 is mounted adjacent the otherend of the connecting member 15 but is electrically insulated frommember 15. Contact point 18 is connected to ground by a suitableconductor and the contact point 17 is connected to the contact point 11by a suitable conductor. A slide member 23 made of conductive materialhas one end fixed to the rotary shaft 7 and its other end slides on theconnecting member 15 and at its end travel bridges connecting points 17and 18 through connecting member 15.

A connecting member 16 of ring-shaped with a gap and which is made ofconductive material is mounted on the substrate 10 coaxially with therotary shaft 7. A contact point is connected to the connecting member 16at one end and is positioned to be opposite to contact point 17. Contactpoint 20 is connected to contact point 12 by a suitable conductor.Adjacent the other end of the connecting member 16, a contact point 19is mounted and it is electrically isolated from the connecting member 16and is to ground by a suitable conductor. A slide contact member 24madeof conductive material has one end fixed to the rotary shaft 7 and itsother end bridges the connecting member 16 and contact points 19 and 20through connecting member 16.

FIG. 4 shows an example of a mixing circuit in which the variableresistor 1 according to the present invention is employed. The slidecontact member 6 is connected to the output terminal and the contactpoints 11 and 12 are connected to the microphone and EQ amplifiers 2 and3, respectively.

With the present invention constructed as above described, if the knob7a is rotated in the direction indicated by the arrow 0 in FIG. 2, theslide contact members 6, 23 and 24 will be rotated together in directiona as shown in FIG. 3. At the extreme counter-clockwise position slidecontact member 6 contacts contact point 11 which connects the microphoneamplifier 2' to the output terminal 4 through only the slide contactmember 6. Also at this position. the slide contact member 24 andconnecting member 16 are connected to contact point 19 whichshort-circuits them to ground. The E0 amplifier 3 is also grounded underthis condition. If the knob 7a is rotated clockwise relative to FIGS.3A, 3B and 3C the slide contact members 6, 23 and 24 will rotatetogether and at the end position slide contact member 6 contacts contactpoint 12 which connects the EQ amplifier 3 to the output terminal 4directly only through the slide contact member 6; Also at this position,slide contact member 23 short-circuits connecting member 15 and thegrounded contact point 18. This grounds the microphone amplifier 2.

If the knob 7a is rotated to a position intermediate such as mid-point con the resistor element 1a as shown in FIG. 4, the slide contact members6, 23 and 24 will be positioned intermediate or at the mid-point onmembers la, 15 and 16, and the output signals from the microphone and EQamplifiers 2 and 3 will be mixed and furnished to the output erminal 4.

As described above, with this invention when the slide contact member 6is rotated to contact either contact point 11 or 12, the signal from themicrophone amplifier 2 or the EQ amplifier 3 will be, respectively,delivered to the output terminal 4 without attenuation. Thus, separationof the two signals is obtained. When the slide contact member 6 ispositioned at an intermediate or mid-point c, the output signals fromthe amplifiers 2 and 3 will be mixed through the resistor body la anddelivered to the output terminal 4 in amounts proportional to theposition of contact 6. The resistance value of the variable resistor lais selected based only on the objective to obtain desired mixture of thetwo signals and its resistance value can be reduced as compared withresistors of the prior art.

In the above example, the substrates 8, 9 and 10 are illustrated asseparate elements, but it is apparent that they can be integrally formedif desired.

FIG. 5 illustrates an example in which the variable resistor of thisinvention is used in a two-channel stereophonic reproduction apparatus.

A description will be given of the left channel (L- channel) of the twochannels system. The output signal from an E0 amplifier 2L whichamplifies the L-channel phono signal is applied to a contact point 11Lwhich is connected to one end of a resistor element 1L of a variableresistor according to this invention. The output from a microphoneamplifier 3 is applied to a contact point 12L at the other end of theresistor element lLa. A slide contact member 6L makes wiper contact withresistor 1L and is connected to an L-channel output terminal 4L. Thestructure and schematic similar to that illustrated in FIGS. 3A, 3B, 3Cand 4 may be used. In FIG. 5, contact points 17L, 18L, 19L, 20L andslide contact members 23L, 24L correspond with contact points 17, 18,19, and 20 and the slide members 23, 24 shown in FIG. 4 and operatesimilarly. That is, when the slide contact member 6L moves upward inFIG. 5 to contact point 11L, the output signal from the microphoneamplifier 3 is connected to ground because it is short-circuited byslide contact member 24L which engages contact point 19L and hence onlythe output signal from the L-channel EQ amplifier 2L is delivered to theoutput terminal 4L. However, when the slide contact member 6L movesdownward in FIG. 5 to engage contact point 12L and the output signalfrom the EQ amplifier 2L is grounded because slide contact 23L engagesgrounded contact point,l8L and hence only the output signal from themicrophone amplifier 3 is delivered to the output terminal 41.. When theslide contact member 6L is intermediate between the contact points 11Land 12L, an output signal which is a mixture of the signals from themicrophone amplifier 3 and the EQ amplifier 2L is delivered to theoutput termianl 4L. Thus, when the slide contact member 6L contactseither of the contact points 11L or 12L, only one of the output signalsfrom the amplifiers will be delivered to the output terminal 4L. Theseparation between the signals is substantially enhanced.

The right channel (R-channel) is constructed and operates substantiallythe same as the L-channel, and the description is omitted for the sakeof brevity. The corresponding elements shown in FIG. 5 are identified bythe same reference numerals as for the left channel except L is changedto R.

In the above-described embodiments when the slide contact memberapproaches one end of the resistor element. the other end of theresistor element is grounded as shown in FIGS. 4 and 5. However, it isalso possible to improve the separation between signals with a structuresuch that when the slide member approaches one end of the resistorelement. the other end of the resistor element is open-circuited. Forthis structure, the variable resistor la of the present invention isconnected as shown in FIG. 6. The output terminal of the microphoneamplifier 2 is connected to the slide contact member 23. Contact point17 is connected to the contact point 11. Contact point 18 is left openedand is not grounded as in FIG. 4. The output terminal of EO amplifier 3is connected to the slide contact member 24. Contact point 20 isconnected to contact point 12. Contact point 19 is left open and is notgrounded as in FIG. 4. Slide contact member 6 is connected to the outputterminal 4.

In FIG. 6. when the slide contact member 6 moves upward relative theFIG. 6 and engages contact point 11, the output signal from themicrophone amplifier 2 is transmitted to the output terminal 4 throughthe slide contact member 23, contact points 17, 11, and the slidecontact member 6 and does not pass through the resistor element la. Atthe same time, the output signal from the EQ amplifier 3 is notfurnished to the output terminal because the slide contact 24 engagesopen contact point 19. Under this condition, contact member 24 does notbridge connection member 16 and contact point 19, but engages onlycontact point 19. When slide contact 6 moves downward relative to theFIG. and engages contact point 12, the output signal from the EQamplifier 3 is transmitted to the output terminal 4 through the slidecontact member 24, contact points 20, 12 and slide contact 6 withoutpassing through the resistor element la. The output signal from themicrophone amplifier 2 is not passed to the output terminal 4 becauseslide contact member 23 engages contact point 18 which is an opencircuit. Under this condition, contact member 23 does not bridgeconnection member 15 and contact point 18, but engages only contactpoint 18.

Thus, separation between the signals can also be improved with theembodiment shown in FIG. 6.

In FIG. 6, when slide contact member 6 engages resistor elementintermediate between contact points 1] and 12, the output signal fromthe microphone amplifier 2 is transmitted through slide contact member23, a part of connecting member (refer to FIG. 3B), the connectingpoints 17, '11, the upper part of the resistor element la relative tothe FIG. and the slide contact member 6 to the output terminal 4. Theoutput signal from the EQ'amplifier 3 is transmitted through slidecontact member 24, a part of connecting member 16 (refer to FIG. 3C).the connecting points 20, 12, the lower part of resistor element 1arelative to the FIG. and the slide contact member 6 to the outputterminal 4. In this case the output signals from the amplifiers 2 and 3are mixed in accordance with the position of the slide contact member 6on the resistor element la and delivered to the output terminal 4.

Thus, in the FIG. 6 embodiment in which when the slide contact member 6contacts one end of the resistor element 1a and the other end is openedcircuit, the same results to that obtained by the embodiment in FIG. 4can be obtained.

A further example of this invention is shown in FIGS. 7 and 8 in whichthe same elements as those shown in FIGS. 4 and 6 are designated by thesame numerals.

A cam 31 which has a projection 31a is fixed to one end of the rotaryshaft 7 which passes through the substrate 8. A switch 32 consists of amovable contact 32a and fixed contacts 32b and 32c is mounted so thatthe movable contact can be actuated by the cam 31. The movable contact32a of the switch 32 is grounded. FIGS. 8A -8C show the connections ofthe FIG. 7 structure. When the knob 7a is rotated either clockwise orcounterclockwise, the movable contact 32a of the switch 32 is moved bycam 31a to contact a first fixed contact 32b (refer to FIG. 8A) oranother fixed contact 320 (refer to FIG. 8C). At these limits of travel.the slide contact member 6 engages either contact point 11 or 12. Whenthe movablecontact 32a does not engage either of the fixed contactpoints 32b and 320, the slide contact member 6 engages resistor elementla between the contact points 11 and 12 (refer to FIG. 8B). Thus, whenthe slide contact member 6 engages one of the contact points 11 and 12,the output signal from a particular amplifier connected to one of thecontact points 11 and 12 is grounded. When the slide contact member 6 isintermediate on the resistor element 1a, the movable contact 32a doesnot contact either of the fixed contacts 32b and 320, and an outputsignal which is from both the amplifiers 2 and 3 (not shown in FIGS. 7and 8) will be produced and delivered to the output terminal 4. It maybe possible to provide a detent mechanism on rotary shaft 7 so thatmovable contact 320 makes positive contact with the fixed contact 32b or320 as projection 31a of the cam 31 engages contact 320. This willassure that the movable contact 32a positively engages contact point 11or 12. It is seen that the example shown in FIGS. 7 and 8A8C producesthe same results as those obtained by the other embodiments.

It will be apparent that many modifications and variations could beeffected by those skilled in the art without departing from the spiritand scope of the novel concepts of the present invention.

We claim as our invention:

1. A variable resistor comprising:

a. a resistor element having first and second terminals;

b. a conductive slide means mounted for slide contact with said resistorelement and said first and second terminals; and

c. switch means controlled by the position of said slide means andoperative to ground one of said first and second terminals of saidresistor element when said slide means engages the other one of saidfirst and second terminals of said resistor element.

2. A variable resistor comprising: a. a resistor element having firstand second terminals;

b. an electrical conductive slide means mounted for slide contact withsaid resistor element and said first and second terminals; and

c. switch means controlled by the position of said slide means andoperable to open the connection between one of said first and secondterminals and said resistor element when said slide means engages theother one of said first and second terminals.

3. A variable resistor comprising:

a. a resistor element having first and second terminals, a first inputsignal source applied to said first terminal, a second input signalsource applied to said second terminal;

b. electrical conductive slide means mounted to slide on said resistorelement between said first and second terminals, an output terminal fordelivering at least one of said first and second signal or a mixedsignal of said input signals connected to said slide means; and

c. switch means controlled by the position of said slide means andoperative to ground one of said first and second input signals when saidslide means engages one of said first and second terminals and to groundthe other one of said first and second input signals when said slidemeans engages the other one of said first and second terminals.

4. A variable resistor comprising:

a. a resistor element having first and second terminals, a first inputsignal applied to said first terminal, a second input signal applied tosaid second terminal;

b. an electrical conductive slide means mounted to slide on saidresistor element between said first and second terminals, said slidemeans supplied at least one of said first and second input signals or amixture thereof from said resistor element depending on the position ofsaid slide means; and

c. switch means controlled by the movement of said slide means andoperative to disconnect one of said first and second input signals fromsaid slide means when said slide means engages one of said first orsecond terminals.

5. A variable resistor comprising:

a. a first resistor element having first and second terminals;

b. a first electrical conductive slide means mounted to slide on saidresistor element between said first and second terminals;

0. a second resistor element having third and fourth terminals;

d. a second electrical conductive slide means mounted to slide on saidsecond resistor element between said third and fourth terminals;

e. first input signal means connected to said first terminal of saidfirst resistor element;

f. second input signal means connected to said fourth terminal of saidsecond resistor body;

g. third input signal means connected to said second and thirdterminals;

h. a first output signal terminal connected to said first slide meansand receiving at least one of said input signals from said first andthird input signal means or a mixture depending upon the position ofsaid first slide means;

i. a second output signal terminal means connected to said second slidemeans and receiving at least one of input signals from said third andfourth input signal means or a mixture depending upon the position ofsaid second slide means;

j. first switch means controlled by movement of said first slide meansand operative to ground one of said first and second terminals of saidfirst resistor element when said first slide means engages the other ofsaid first and second terminals; and

k. second switch means controlled by movement of said second slide meansand operative to ground one of said third and fourth terminals of saidsecond resistor element when said second slide means engages the otherof said third and fourth terminals.

6. A variable resistor comprising:

a. a first substrate;

b. a rotary shaft rotatably supported by said first substrate;

c. a resistor element generally ring-shaped formed with a gap mounted onsaid first substrate around said rotary shaft, said resistor elementhaving first and second contact points at opposite ends;

d. a first slide means with one end attached to said rotary shaft andslidable on said resistor element between said first and second contactpoints;

e. a second substrate rotatably supporting said rotary shaft;

f. a first connecting member generally ring-shaped with a gap mounted onsaid second substrate around said rotary shaft, said first connectingmember having a third contact point at one end thereof;

g. a fourth grounded contact point mounted on said second substrateadjacent the other end of said first connecting member and electricallyisolated from said first connecting member;

h. second slide means with one end attached to said rotary shaft andslidable on said first connecting member between said third and fourthcontact points i. a third substrate rotatably supporting said rotaryshaft;

j. a second connecting member generally ring-shaped with a gap mountedon said third substrate around said rotary shaft, said second connectingmember having a fifth contact on one end corresponding to the positionof said third contact relative to rotation of said rotary shaft;

k. a sixth grounded contact point mounted on said second substrateadjacent the other end of said second connecting member and electricallyisolated from said second connecting member;

1. third slide means with one end fixed to said rotary shaft andslidable on said second connecting member between said fifth and sixthcontact points; and

said switch means is a cam switch having at least three contact pointsone of which is grounded, and said cam switch controlled by the positionof said slide means.

1. A variable resistor comprising: a. a resistor element having firstand second terminals; b. a conductive slide means mounted for slidecontact with said resistor element and said first and second terminals;and c. switch means controlled by the position of said slide means andoperative to ground one of said first and second terminals of saidresistor element when said slide means engages the other one of saidfirst and second terminals of said resistor element.
 2. A variableresistor comprising: a. a resistor element having first and secondterminals; b. an electrical conductive slide means mounted for slidecontact with said resistor element and said first and second terminals;and c. switch means controlled by the position of said slide means andoperable to open the connection between one of said first and secondterminals and said resistor element when said slide means engages theother one of said first and second terminals.
 3. A variable resistorcomprising: a. a resistor element having first and second terminals, afirst input signal source applied to said first terminal, a second inputsignal source applied to said second terminal; b. electrical conductiveslide means mounted to slide on said resistor element between said firstand second terminals, an output terminal for delivering at least one ofsaid first and second signal or a mixed signal of said input signalsconnected to said slide means; and c. switch means controlled by theposition of said slide means and operative to ground one of said firstand second input signals when said slide means engages one of said firstand second terminals and to ground the other one of said first andsecond input signals when said slide means engages the other one of saidfirst and second terminals.
 4. A variable resistor comprising: a. aresistor element having first and second terminals, a first input signalapplied to said first terminal, a second input signal applied to saidsecond terminal; b. an electrical conductive slide means mounted toslide on said resistor element between said first and second terminals,said slide means supplied at least one of said first and second inputsignals or a mixture thereof from said resistor element depending on theposition of said slide means; and c. switch means controlled by themovement of said slide means and operative to disconnect one of saidfirst and second input signals from said slide means when said slidemeans engages one of said first or second terminals.
 5. A variableresistor comprising: a. a first resistor element having first and secondterminals; b. a first electrical conductive slide means mounted to slideon said resistor element between said first and second terminals; c. asecond resistor element having third and fourth terminals; d. a secondelectrical conductive slide means mounted to slide on said secondresistor element between said third and fourth terminals; e. first inputsignal means connected to said first terminal of said first resistorelemenT; f. second input signal means connected to said fourth terminalof said second resistor body; g. third input signal means connected tosaid second and third terminals; h. a first output signal terminalconnected to said first slide means and receiving at least one of saidinput signals from said first and third input signal means or a mixturedepending upon the position of said first slide means; i. a secondoutput signal terminal means connected to said second slide means andreceiving at least one of input signals from said third and fourth inputsignal means or a mixture depending upon the position of said secondslide means; j. first switch means controlled by movement of said firstslide means and operative to ground one of said first and secondterminals of said first resistor element when said first slide meansengages the other of said first and second terminals; and k. secondswitch means controlled by movement of said second slide means andoperative to ground one of said third and fourth terminals of saidsecond resistor element when said second slide means engages the otherof said third and fourth terminals.
 6. A variable resistor comprising:a. a first substrate; b. a rotary shaft rotatably supported by saidfirst substrate; c. a resistor element generally ring-shaped formed witha gap mounted on said first substrate around said rotary shaft, saidresistor element having first and second contact points at oppositeends; d. a first slide means with one end attached to said rotary shaftand slidable on said resistor element between said first and secondcontact points; e. a second substrate rotatably supporting said rotaryshaft; f. a first connecting member generally ring-shaped with a gapmounted on said second substrate around said rotary shaft, said firstconnecting member having a third contact point at one end thereof; g. afourth grounded contact point mounted on said second substrate adjacentthe other end of said first connecting member and electrically isolatedfrom said first connecting member; h. second slide means with one endattached to said rotary shaft and slidable on said first connectingmember between said third and fourth contact points, i. a thirdsubstrate rotatably supporting said rotary shaft; j. a second connectingmember generally ring-shaped with a gap mounted on said third substratearound said rotary shaft, said second connecting member having a fifthcontact on one end corresponding to the position of said third contactrelative to rotation of said rotary shaft; k. a sixth grounded contactpoint mounted on said second substrate adjacent the other end of saidsecond connecting member and electrically isolated from said secondconnecting member; l. third slide means with one end fixed to saidrotary shaft and slidable on said second connecting member between saidfifth and sixth contact points; and m. means connecting said firstcontact point with said third contact point and said second contactpoint with said sixth contact point.
 7. A variable resistor according toclaim 3, wherein said switch means is a cam switch having at least threecontact points one of which is grounded, and said cam switch controlledby the position of said slide means.